PROJECT SUMMARY This project will continue a productive academic-industrial partnership between Dartmouth and Medtronic through which Dartmouth?s intraoperative image updating techniques have already been merged with Med- tronic?s state-of-the-art S7 navigation system to produce and visualize updated MR (uMR) images concurrent with surgery. In a second funding period, we will fully validate and prospectively evaluate uMRs in open-cranial surgery via comparisons with intraoperative MR (iMR). We also propose a new direction: generating uMR to guide minimally invasive neurosurgeries as a possible low-cost, yet effective, alternative to in-bore MR- guidance (new preliminary results of image-updating in minimally-invasive deep brain stimulation indicate feas- ibility and suggest promise). While validation studies completed to date with a tracked stylus as ?ground truth? have been impressive, relatively few points are available at any given time during surgery, and tracking and feature identification/localization errors are embedded in the TRE (target registration error) results. Thus, a cornerstone of our continuation proposal is validation with iMR, which is available in Dartmouth?s Center for Surgical Innovation (CSI). Since iMR is deployed at end-of-resection to survey for residual disease in open cranial surgery and multiple iMRs are difficult to justify because of patient safety concerns, we have proposed a new large animal glioma model which has been developed successfully in our hands (we can now grow solid tumors of varying size and shape located in different intra-cranial positions) in which iMR will be acquired multiple times during a resection procedure for uMR validation. These animal studies are also ideally-suited to minimally-invasive cases because we can determine the image-updating requirements to guide the procedure as a more efficient and cost-effective alternative to iMR. CSI can accommodate these experiments, and as a result, we are in a unique position to conduct animal and human studies in the same space with the same navigation/imaging equipment for uMR validation with iMR under both open cranial and minimally invasive conditions. Based on progress to date, and these considerations, we propose technical advances that will apply image-updating to minimally-invasive neurosurgical procedures, accelerate image-updating through GPU processing, and add uMR data into the surgeon?s heads-up display; validation in large animal glioma open- cranial and minimally-invasive studies where iMR acquisitions are not limited, and during similar human brain tumor cases where iMR use is restricted; and prospective evaluation of end-of-resection surgical accuracy of procedures navigated with preoperative MR (pMR) to those where uMR is also available. By the end of the proposed 2nd funding period, we will have an uMR guidance platform that is fully validated for open cranial and minimally-invasive procedures, and will have demonstrated the extent to which it enables neurosurgeons to achieve more accurate open-cranial resections more often, and whether it is sufficiently accurate and timely for guidance of minimally-invasive neurosurgical interventions relative to in-bore MR guidance.